Mediation effect of cardiorespiratory fitness on relationships between high-intensity interval training and body fat in overweight and obese adolescents

BACKGROUND: High-intensive interval training (HIIT) is an effective way to reduce body fat. Numerous studies confirmed the effectiveness of the HIIT for cardiorespiratory fitness development. Fewer studies examined the relationship between these factors in one dependencies model in overweight and obese adolescents. Therefore, the main aim of this study was to examine whether cardiorespiratory fitness mediated the relationship between HIIT and body fat% and whether sex moderated this relation. METHODS: Thirty-six students (15 boys and 21 girls) aged 16.02±0.39 years were examined. Participants were assigned to the HIIT intervention or control group. The intervention lasted 14 minutes during one physical education lesson per week for ten weeks. Harvard step-test results which reflected cardiorespiratory fitness and body fat% received via bioimpedance, were analyzed. RESULTS: Mediation analysis was conducted in the whole group because sex was not a moderator in any associations (P>0.05). HIIT intervention was associated with reducing body fat% (B=-3.63, P=0.029) and improvement of cardiorespiratory fitness (B=4.487, P<0.001). Simultaneously, body fat% was significantly mediated by changes in cardiorespiratory fitness (B=-2.21, P<0.049). Significant effect of HIIT on body fat% decreased (Bdirecttotal) and was no longer significant after including cardiorespiratory fitness (B=-1.42, P=0.431). CONCLUSIONS: HIIT training is an effective method of reducing body fat% and improving cardiorespiratory fitness. A higher cardiorespiratory fitness level may be conducive to increase the effectiveness of HIIT training, which translates into a more effective reduction of body fat. Due to the lack of sex moderation in the observed relationships, this effect occurs in both sexes.